A high-strength, corrosion-resistant martensitic aging steel powder for injection molding and high-strength, corrosion-resistant martensitic aging steel prepared therefrom.

Abstract

The application relates to the field of powder metallurgy materials and intelligent manufacturing technology, in particular to a high-strength corrosion-resistant maraging steel powder for injection molding and a high-strength corrosion-resistant maraging steel prepared by using the same. The mass percentage content of each chemical element of the high-strength corrosion-resistant maraging steel powder for injection molding is as follows: 17-19wt% of Ni, 12-13wt% of Cr, 5-5.5wt% of Mo, 1.4-1.6wt% of Ti, 0.3-0.5wt% of Al, 0.05-0.1wt% of N, 0.15-0.30wt% of O, C: <=0.02, the balance of Fe, and inevitable impurity elements. The high-strength corrosion-resistant maraging steel prepared by the application meets the extreme requirements of high strength (>=1800MPa), high plasticity (elongation 4.0-5.4%) and high salt mist corrosion resistance (>=4 hours).

Description

Technical Field

[0001] This invention relates to the fields of powder metallurgy materials and intelligent manufacturing technology, and in particular to a high-strength corrosion-resistant martensitic aging steel powder for injection molding and a high-strength corrosion-resistant martensitic aging steel prepared therefrom. Background Technology

[0002] Martensitic aging steel is a type of ultra-high strength steel. Due to its high strength, high toughness, and good weldability, it is widely used in aerospace, marine development, and military fields. A key advantage of martensitic aging steel is its simple and convenient heat treatment process. After solution treatment, it undergoes machining before aging, resulting in minimal deformation and excellent machinability and weldability.

[0003] Metal injection molding (MIM) is a new production process that combines the characteristics of powder metallurgy and injection molding. It uses metal powder and binder as raw materials, mixes the powder and binder evenly at a certain temperature using an appropriate method, feeds the mixture into a granulated form, and then injects it into shape. Finally, it is debound and sintered. It is suitable for the preparation and mass production of complex structural parts.

[0004] Metal injection molding (MIM) technology can be used to process most metals and alloys that can be made into powder. It is widely applicable to the production of small, three-dimensional complex shapes and products with special performance requirements. The basic process of metal injection molding generally includes the following steps: First, select metal powder and binder that meet the requirements of MIM. Then, mix the powder and binder into a uniform feed at a certain temperature using an appropriate method. After granulation, the feed is injected and molded. The resulting preform is degreased and then sintered to densify, becoming the final product.

[0005] While commercially available 1750MPa martensitic aging steel prepared by existing metal injection molding processes meets application requirements in terms of mechanical properties, its corrosion resistance is poor, with a salt spray protection time of only 1 hour (GB / T 10125-2021). Furthermore, 18Ni300 martensitic aging steel prepared from 18Ni300 powder via metal injection molding also exhibits poor corrosion resistance (salt spray protection time of 1 hour, GB / T 10125-2021), and its density is relatively low (96.0-97.5%), resulting in lower mechanical properties compared to traditionally cast 18Ni300 martensitic aging steel.

[0006] To this end, the inventors developed a high-strength, corrosion-resistant martensitic aging steel powder for injection molding and a high-strength, corrosion-resistant martensitic aging steel prepared using the powder. Summary of the Invention

[0007] To address the technical problems existing in current hydrogen storage technologies, this invention provides a high-strength, corrosion-resistant martensitic aging steel powder for injection molding and a high-strength, corrosion-resistant martensitic aging steel prepared using the powder.

[0008] The present invention provides a high-strength, corrosion-resistant martensitic aging steel powder for injection molding, which is achieved through the following technical solution:

[0009] The mass percentage content of each chemical element in a high-strength corrosion-resistant martensitic aging steel powder for injection molding is as follows: 17-19 wt% Ni, 12-13 wt% Cr, 5.0-5.5 wt% Mo, 1.4-1.6 wt% Ti, 0.3-0.5 wt% Al, 0.05-0.10 wt% N, 0.15-0.30 wt% O, C ≤ 0.02, balance Fe, and unavoidable impurity elements.

[0010] During the synergistic sintering process, 12–13 wt% Cr and 0.05–0.10 wt% N form a Cr2O3-CrN-Al2O3 gradient composite film; 5.0–5.5 wt% Mo inhibits grain boundary migration, replacing the eutectic liquid phase to achieve diffusion densification; 1.4–1.6 wt% Ti and 0.3–0.5 wt% Al reduce interfacial segregation, prevent precipitates from penetrating the passivation film, and improve the corrosion resistance of the passivation film.

[0011] The high-strength and corrosion-resistant martensitic aging steel powder of this invention is suitable for metal powder injection molding process. The high-strength and corrosion-resistant martensitic aging steel prepared meets the extreme requirements of high-precision and complex parts such as aerospace, medical devices, 3C electronic structural components, and marine equipment for strength (≥1800MPa), plasticity (elongation 4.0~5.4%), and salt spray corrosion resistance (≥4 hours).

[0012] Preferably, the mass percentage content of each chemical element in the high-strength corrosion-resistant martensitic aging steel powder for injection molding is as follows: 17.5–18.5 wt% Ni, 12.6–13.0 wt% Cr, 5.3–5.5 wt% Mo, 1.4–1.5 wt% Ti, 0.38–0.42 wt% Al, 0.05–0.07 wt% N, 0.18–0.24 wt% O, C ≤ 0.02, with the balance being Fe, and unavoidable impurity elements.

[0013] Preferably, the high-strength, corrosion-resistant martensitic aging steel powder for injection molding is prepared by gas atomization, with D10 of 1-2 μm, D50 of 2-10 μm, D90 of 8-15.5 μm, loose density of 3-4 g / cm3, and tap density of 4.2-4.8 g / cm3.

[0014] More preferably, the high-strength corrosion-resistant martensitic aging steel powder for injection molding is prepared by gas atomization, with D10 of 1.6±0.1μm, D50 of 8±0.2μm, D90 of 15±0.5μm, loose density of 3.2±0.2g / cm3, and tap density of 4.5±0.2g / cm3.

[0015] Smaller particle size of high-strength, corrosion-resistant, martensitic aging steel powder for injection molding results in a larger specific surface area, which improves sintering activity, promotes sintering, and enhances the mechanical properties of high-strength, corrosion-resistant martensite.

[0016] The present invention provides a high-strength, corrosion-resistant martensitic aging steel prepared using high-strength, corrosion-resistant martensitic aging steel powder for injection molding, which is achieved through the following technical solution:

[0017] A high-strength corrosion-resistant maraging steel prepared using high-strength corrosion-resistant maraging steel powder for injection molding is made by metal powder injection molding process using 90-91 wt% high-strength corrosion-resistant maraging steel powder for injection molding and 9-10 wt% binder.

[0018] Preferably, the preparation method of the high-strength, corrosion-resistant martensitic aging steel is as follows:

[0019] S1. Preparation of high-strength, corrosion-resistant martensitic aging steel powder for injection molding:

[0020] S2. Mixing: Mix the high-strength corrosion-resistant martensitic aging steel powder for injection molding in S1 with the binder at a mass ratio of (90-91):(9-10) to obtain the high-strength corrosion-resistant martensitic aging steel feedstock;

[0021] S3. Injection molding: The high-strength, corrosion-resistant, martensitic aging steel obtained in S2 is injected into the mold through an injection molding machine, cooled and shaped to obtain a blank;

[0022] S4. Catalytic degreasing: The catalyst is 98% fuming nitric acid, the temperature is 110~120℃, the acid inlet rate is 4~6ml / min, and the nitric acid degreasing time is 300±30min;

[0023] S5. Sintering process: Place the blank that has undergone catalytic degreasing in a graphite vacuum sintering furnace, under argon conditions, with an argon flow rate of 5-15L / min, and heat to 1350-1400℃ at a rate of 1-20℃ / min, and hold for 3-5 hours.

[0024] S6. Cool down to 900℃ at 6.5-8.4℃ / min, introduce nitrogen-oxygen mixture at a flow rate of 10-20L / min, and the oxygen content in the nitrogen-oxygen mixture is 0.30±0.02%v. After continuously introducing nitrogen-oxygen mixture for 100-150min, the sintered blank is cooled from 900℃ to room temperature.

[0025] S7. Heat Treatment:

[0026] ①Solid solution repair: Under vacuum conditions, the heating rate is 10±2℃ / min, the temperature is raised from room temperature to 1100±20℃, held for 60±5min, and then nitrogen gas at 0.8±0.1MPa is introduced to cool to room temperature at a cooling rate of 20±5℃ / min.

[0027] ② Two-stage aging: Under vacuum conditions, the heating rate is 10±2℃ / min, the temperature is raised from room temperature to 440-450℃, and held for 10±2h; the heating rate is 10±2℃ / min, the temperature is raised from 440-450℃ to 480-490℃, and held for 180±10min, and then nitrogen gas at 0.2±0.05MPa is introduced to cool to room temperature at a cooling rate of 10±2℃ / min;

[0028] ③ Nitriding repair: Under a nitrogen atmosphere, the heating rate is 10±2℃ / min, and the temperature is raised from room temperature to 400±5℃. The temperature is held for 60±5min, and then nitrogen gas at 0.2±0.05MPa is introduced to cool the temperature back to room temperature at a cooling rate of 10±2℃ / min. This yields high-strength, corrosion-resistant, martensitic aging steel.

[0029] Compared with the traditional production process of 18Ni300 martensitic aging steel, the preparation process of the high-strength corrosion-resistant martensitic aging steel in this invention has the advantages of safety and environmental protection. The entire process is CO / H2-free, reducing the risk of explosion and the cost of exhaust gas treatment. Moreover, the process is simplified, and the sintering produces a self-generated passivation film, eliminating the need for passivation, electroplating, spraying and other processes, which can effectively save costs.

[0030] The resulting high-strength, corrosion-resistant martensitic aging steel has a maximum tensile force ≥16kN, tensile strength ≥2000MPa, yield strength ≥1800MPa, hardness of 50-54HRC, elongation of 4.8-5.5%, salt spray protection time ≥4h, and ISO 5 level.

[0031] Preferably, the S5 sintering process involves placing the catalytically degreased blank in a graphite vacuum sintering furnace, under argon conditions with an argon flow rate of 5-15 L / min, heating to 1360℃ at a rate of 20℃ / min, and holding for 3.0 h.

[0032] By adopting the above technical solution, the pore closure rate of the sintered blank can be >99.0%, which improves the density and mechanical properties of high-strength corrosion-resistant martensitic aging steel.

[0033] Preferably, in step S6, the temperature is lowered to 900°C at a rate of 7.6-7.7°C / min, and a nitrogen-oxygen mixture is introduced at a flow rate of 15 L / min. The oxygen content in the nitrogen-oxygen mixture is 0.30%v. After the nitrogen-oxygen mixture is continuously introduced for 120 min, the sintered blank is cooled from 900°C to room temperature.

[0034] By adopting the above technical solution, the oxygen concentration in the nitrogen-oxygen mixture is precisely controlled to 0.3%v in the cooling section, ensuring that the formed passivation film is dense and crack-free, with a passivation film thickness of 65±5nm, salt spray protection time ≥4h, ISO level 5, and a small amount of red rust on the surface (no substrate corrosion).

[0035] Preferably, the solid solution repair in S7 is carried out under vacuum conditions at a heating rate of 10±0.5℃ / min, from room temperature to 1100℃, and held for 60 min. Then, nitrogen gas at 0.8±0.05MPa is introduced to cool to room temperature at a cooling rate of 20±0.5℃ / min.

[0036] Without the participation of H2, solid solution repair can thermally activated diffusion repair of membrane defects and improve the quality of passivation membrane; and the entire process is CO / H2-free, reducing the risk of explosion and the cost of exhaust gas treatment.

[0037] Preferably, the two-stage aging process in S7 is as follows: under vacuum conditions, the heating rate is 10±0.5℃ / min, the temperature is raised from room temperature to 440℃, and held for 10h; the heating rate is 10±0.5℃ / min, the temperature is raised from 440℃ to 485℃, and held for 180min, and then nitrogen gas at 0.2±0.05MPa is introduced to cool to room temperature at a cooling rate of 10±0.5℃ / min.

[0038] Two-stage aging can lock in Ti diffusion at low temperatures: Ni3Ti nucleates inside the matrix away from the interface, precipitates avoid the film layer, and the passivation film is dense and crack-free, thus ensuring the overall corrosion resistance. However, single-stage aging >460℃ will lead to a decrease in the salt spray precipitation time at the Ni3Ti interface, affecting the overall corrosion resistance.

[0039] Preferably, the nitriding repair in S7 is carried out in a nitrogen atmosphere at a heating rate of 10±0.5℃ / min, from room temperature to 400℃, and held for 60min. Then, nitrogen gas at 0.2±0.05MPa is introduced to cool the temperature back to room temperature at a cooling rate of 10±0.5℃ / min.

[0040] In nitriding repair, N2 fills oxygen vacancies: increases the Cr concentration in the film, improves the quality of the passivation film, and thus improves the overall corrosion resistance.

[0041] In summary, the present invention has the following advantages:

[0042] 1. The high-strength corrosion-resistant martensitic aging steel of this invention has a maximum tensile force ≥16kN, tensile strength ≥2000MPa, yield strength ≥1800MPa, hardness of 50-54HRC, elongation of 4.8-5.5%, and salt spray protection time ≥4h.

[0043] 2. The high-strength corrosion-resistant maraging steel powder for injection molding in this invention uses 12.6-13.0wt%Cr+0.38-0.42wt%Al+0.05-0.07wt%N as the core film-forming elements and forms a dense Cr2O3-CrN-Al2O3 composite passivation film by passing a N2 / O2 (O2 content is 0.3±0.02%v) mixed gas through the sintering cooling section. This effectively improves the corrosion resistance of the maraging steel, with a salt spray protection time ≥4h and ISO 5 level.

[0044] 3. The preparation process of the high-strength corrosion-resistant martensitic aging steel in this invention has the advantages of safety and environmental protection compared with the traditional production process of 18Ni300 martensitic aging steel. The entire process is free of CO / H2, reducing the risk of explosion and the cost of exhaust gas treatment.

[0045] 4. Compared with the traditional production process of 18Ni300 martensitic aging steel, the preparation process of the high-strength corrosion-resistant martensitic aging steel in this invention simplifies the process, sintersing a self-generated passivation film, eliminating the need for passivation, electroplating, spraying and other processes, which can effectively save costs.

[0046] 5. The passivation film of the high-strength corrosion-resistant martensitic aging steel in this invention is long-lasting and stable, with a salt spray protection time of ≥4h, ISO 5 level, and nitriding repair solves the problem of chromium depletion in precipitates. Attached Figure Description

[0047] Figure 1 This is a 200x metallographic image of the high-strength, corrosion-resistant, martensitic aging steel in Example 1.

[0048] Figure 2 This is a magnified image of the surface rust spots of the high-strength, corrosion-resistant, martensitic aging steel in Example 1 after a 2-hour salt spray test.

[0049] Figure 3 This is a magnified image of the surface rust spots of the high-strength, corrosion-resistant, martensitic aging steel in Example 1 after a 4-hour salt spray test.

[0050] Figure 4 This is a SEM image of the high-strength, corrosion-resistant, martensitic aging steel after heat treatment at 440℃×10h+485℃×3h in Example 1.

[0051] Figure 5 This is the stress-strain curve of the high-strength corrosion-resistant martensitic aging steel in Example 1.

[0052] Figure 6 This is a 200x metallographic image of the high-strength, corrosion-resistant, martensitic aging steel in Comparative Example 1.

[0053] Figure 7 This is a magnified image of the surface rust spots of the high-strength corrosion-resistant martensitic aging steel in Comparative Example 1 after a 2-hour salt spray test.

[0054] Figure 8 This is a SEM image of the high-strength, corrosion-resistant, martensitic aging steel in Comparative Example 1 after heat treatment at 485℃ for 13 hours.

[0055] Figure 9 This is a 500x magnified view of a slice of martensitic aging steel after S4 sintering in Comparative Example 1.

[0056] Figure 10 This is the stress-strain curve of the high-strength corrosion-resistant martensitic aging steel in Comparative Example 1. Detailed Implementation

[0057] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, comparative examples and embodiments.

[0058] Example: The mass percentage content of each chemical element in the high-strength corrosion-resistant martensitic aging steel powder for injection molding is as follows: 17-19 wt% Ni, 12-13 wt% Cr, 5.0-5.5 wt% Mo, 1.4-1.6 wt% Ti, 0.3-0.5 wt% Al, 0.05-0.10 wt% N, 0.15-0.30 wt% O, C ≤ 0.02, balance Fe, and unavoidable impurity elements.

[0059] Preferably, the mass percentage content of each chemical element in the high-strength corrosion-resistant martensitic aging steel powder for injection molding is as follows: 17.5–18.5 wt% Ni, 12.6–13.0 wt% Cr, 5.3–5.5 wt% Mo, 1.4–1.5 wt% Ti, 0.38–0.42 wt% Al, 0.05–0.07 wt% N, 0.18–0.24 wt% O, C ≤ 0.02, balance Fe, and unavoidable impurity elements.

[0060] High-strength, corrosion-resistant martensitic aging steel powder for injection molding is prepared by gas atomization. It has a density of D10 of 1–2 μm, D50 of 2–10 μm, D90 of 8–15.5 μm, a loose packing density of 3–4 g / cm³, and a tapped density of 4.2–4.8 g / cm³. Preferably, the high-strength, corrosion-resistant martensitic aging steel powder for injection molding has a D10 of 1.6 ± 0.1 μm, a D50 of 8 ± 0.2 μm, a D90 of 15 ± 0.5 μm, a loose packing density of 3.2 ± 0.2 g / cm³, and a tapped density of 4.5 ± 0.2 g / cm³.

[0061] Specifically, the mass percentage content of each chemical element in the high-strength corrosion-resistant maraging steel powder for injection molding is as follows: 17.52 wt% Ni, 12.77 wt% Cr, 5.43 wt% Mo, 1.44 wt% Ti, 0.40 wt% Al, 0.053 wt% N, 0.21 wt% O, 0.002 wt% C, with the balance being Fe, and unavoidable impurities. The high-strength corrosion-resistant maraging steel powder for injection molding has a D10 of 1.61 μm, a D50 of 8.03 μm, a D90 of 15.43 μm, a loose packing density of 3.22 g / cm³, and a tapped density of 4.45 g / cm³.

[0062] A high-strength corrosion-resistant maraging steel prepared using high-strength corrosion-resistant maraging steel powder for injection molding is made by metal powder injection molding process using 90-91 wt% high-strength corrosion-resistant maraging steel powder for injection molding and 9-10 wt% binder.

[0063] The adhesive is prepared as follows: 85g of polyoxymethylene F20-03 (POM, Mitsubishi Engineering F20-03, general grade), 6.5g of HDPE (NOVA high-density polyethylene, injection molding grade), 4g of 30E783 maleic anhydride grafted EVA (compatibilizer EVA, DuPont 30E783 maleic anhydride grafted EVA, molding grade), 2g of PETS plastic lubricant BRD-PETS (PETS plastic lubricant, model BRD-PETS, brand: Boruida), and 1.5g of dispersant stearic acid (dispersant stearic acid, CAS: 57-11-4, brand: Lvbao) are mixed at 500rpm for 10min to obtain the adhesive.

[0064] A method for preparing high-strength, corrosion-resistant martensitic aging steel using injection molding high-strength, corrosion-resistant martensitic aging steel powder includes the following steps:

[0065] S1. Preparation of high-strength, corrosion-resistant martensitic aging steel powder for injection molding:

[0066] S2. Mixing: Mix the high-strength corrosion-resistant martensitic aging steel powder for injection molding in S1 with the binder at a mass ratio of (90-91):(9-10) to obtain the high-strength corrosion-resistant martensitic aging steel feedstock;

[0067] S3. Injection molding: The high-strength, corrosion-resistant, martensitic aging steel obtained in S2 is injected into the mold through an injection molding machine, cooled and shaped to obtain a blank;

[0068] S4. Catalytic degreasing: The catalyst is 98% fuming nitric acid, the temperature is 110-120℃, the acid inlet rate is 4-6 ml / min, and the nitric acid degreasing time is 300±30 min;

[0069] S5. Sintering process: Place the blank that has undergone catalytic degreasing in a graphite vacuum sintering furnace, under argon conditions, with an argon flow rate of 5-15L / min, and heat to 1350-1400℃ at a rate of 1-20℃ / min, and hold for 3-5 hours.

[0070] S6. Cool down to 900℃ at 6.5-8.4℃ / min, introduce nitrogen-oxygen mixture at a flow rate of 10-20L / min, and the oxygen content in the nitrogen-oxygen mixture is 0.30±0.02%v. After continuously introducing nitrogen-oxygen mixture for 100-150min, the sintered blank is cooled from 900℃ to room temperature.

[0071] S7. Heat treatment: ① Solution repair: Under vacuum conditions, the heating rate is 10±2℃ / min, the temperature is raised from room temperature to 1100±20℃, held for 60±5min, and then nitrogen gas of 0.8±0.1MPa is introduced to cool to room temperature at a cooling rate of 20±5℃ / min.

[0072] ② Two-stage aging: Under vacuum conditions, the heating rate is 10±2℃ / min, the temperature is raised from room temperature to 440-450℃, and held for 10±2h; the heating rate is 10±2℃ / min, the temperature is raised from 440-450℃ to 480-490℃, and held for 180±10min, and then nitrogen gas at 0.2±0.05MPa is introduced to cool to room temperature at a cooling rate of 10±2℃ / min;

[0073] ③ Nitriding repair: Under a nitrogen atmosphere, the heating rate is 10±2℃ / min, and the temperature is raised from room temperature to 400±5℃. The temperature is held for 60±5min, and then nitrogen gas at 0.2±0.05MPa is introduced to cool the temperature back to room temperature at a cooling rate of 10±2℃ / min. This yields high-strength, corrosion-resistant, martensitic aging steel.

[0074] Example 1: A method for preparing high-strength, corrosion-resistant martensitic aging steel using injection molding high-strength, corrosion-resistant martensitic aging steel powder, comprising the following steps:

[0075] S1. High-strength, corrosion-resistant martensitic aging steel powder for injection molding was prepared by gas atomization. The mass percentage content of each chemical element is as follows: 17.52 wt% Ni, 12.77 wt% Cr, 5.43 wt% Mo, 1.44 wt% Ti, 0.40 wt% Al, 0.053 wt% N, 0.21 wt% O, 0.002 wt% C, balance Fe, and unavoidable impurity elements; D10 is 1.61 μm, D50 is 8.03 μm, D90 is 15.43 μm, loose density is 3.22 g / cm3, and tap density is 4.45 g / cm3.

[0076] S2. Mixing: The high-strength corrosion-resistant martensitic aging steel powder for injection molding in S1 and the binder are added to the internal mixer at a mass ratio of 90.9:9.1 and mixed. The mixing temperature is 190℃, the mixing time is 60min, and the screw speed of the internal mixer is 30r / min to obtain the high-strength corrosion-resistant martensitic aging steel feed.

[0077] S3, Injection Molding: The high-strength, corrosion-resistant martensitic aging steel obtained in S2 is injected into the mold through an injection molding machine. The injection molding parameters of the injection molding machine are as follows: Injection machine type: hydraulic press; Injection material temperature: nozzle 190℃, second stage 185℃, third stage 180℃, fourth stage 170℃; Mold temperature: 105℃; Injection speed: first stage 40%, second stage 40%; Molding pressure: first stage 80%, second stage 85%; Holding pressure: 60%; Holding time: 1s; Back pressure: 4bar; Cooling time: 10s. After cooling and molding, a blank is obtained.

[0078] S4. Catalytic degreasing: The catalyst is 98% fuming nitric acid, the temperature is 115℃, the acid inlet rate is 5ml / min, and the degreasing time is 300min;

[0079] S5. Sintering Process: The catalytically degreased blank is placed in a graphite vacuum sintering furnace under argon atmosphere (argon flow rate 10 L / min) for sintering. The sintering procedure for the graphite vacuum sintering furnace is as follows:

[0080] ① Heating rate is 5℃ / min, room temperature → 300℃, hold for 30min;

[0081] ② The heating rate is 2℃ / min, from 300℃ to 450℃, and the temperature is maintained for 30 minutes;

[0082] ③ The heating rate is 2℃ / min, from 450℃ to 600℃, and the temperature is maintained for 60 minutes;

[0083] ④ Heating rate is 3℃ / min, 600℃→1050℃, hold for 20min;

[0084] ⑤ The heating rate is 10℃ / min, from 1050℃ to 1250℃, and the temperature is maintained for 120min;

[0085] ⑥ The cooling rate is 7.5℃ / min, from 1250℃ to 800℃;

[0086] ⑦ The cooling rate is 12℃ / min, from 800℃ to 80℃;

[0087] S6. Air cooling: After 60 minutes, the temperature drops from 1360℃ to 900℃. A nitrogen-oxygen mixture is introduced at a flow rate of 15L / min and an oxygen content of 0.30%v. After the nitrogen-oxygen mixture is continuously introduced for 2 hours, the sintered blank is cooled from 900℃ to room temperature.

[0088] S7. Heat Treatment:

[0089] ①Solid solution repair: Under vacuum conditions, the heating rate is 10℃ / min, the temperature is raised from room temperature to 1100℃, held for 60min, and then nitrogen gas at 0.8MPa is introduced to cool to room temperature at a cooling rate of 20℃ / min, 1100℃→room temperature;

[0090] ② Two-stage aging: Under vacuum conditions, the heating rate is 10℃ / min, the temperature is raised from room temperature to 440℃, and held for 10h; the heating rate is 10℃ / min, the temperature is raised from 440℃ to 485℃, and held for 180min, then nitrogen gas at a pressure of 0.2MPa is introduced to cool to room temperature at a cooling rate of 10℃ / min, 485℃→room temperature;

[0091] ③ Nitriding repair: Under a nitrogen atmosphere, the heating rate is 10℃ / min, the temperature is raised from room temperature to 400℃, and held for 60min. Then, nitrogen gas at a pressure of 0.2MPa is introduced to cool to room temperature at a cooling rate of 10℃ / min. The temperature is then changed from 400℃ to room temperature, and high-strength corrosion-resistant martensitic aging steel can be obtained.

[0092] Comparative Example 1: Commercial 1750MPa grade martensitic aging steel was made by metal powder injection molding process using 90.9wt% of commercially available martensitic aging steel powder and 9.1wt% of binder.

[0093] The commercially available maraging steel powder contains the following mass percentages of chemical elements: 0.003 wt% C, 0.306 wt% O, 0.260 wt% Mn, 6.69 wt% Ni, 5.78 wt% Mo, 8.31 wt% Cr, 14.99 wt% Co, 0.254 wt% Si, with the balance being Fe. Its density is as follows: D10 is 2.464 μm, D50 is 7.527 μm, D90 is 19.79 μm, loose density is 3.22 g / cm³, and tap density is 4.68 g / cm³. This commercially available maraging steel powder is supplied by Hebei Jingye Lide Additive Manufacturing Co., Ltd.

[0094] The preparation method of commercial 1750MPa grade martensitic aging steel is as follows:

[0095] S1. Mixing: Add martensitic aging steel powder and binder to a mixer at a mass ratio of 90.9:9.1 and mix at a mixing temperature of 190℃ for 60 minutes and a screw speed of 30 r / min to obtain martensitic aging steel feed.

[0096] S2. Injection Molding: The martensitic aging steel obtained in S1 is injected into the mold through an injection molding machine. The injection molding parameters of the injection molding machine are as follows: Injection machine type: hydraulic press; Injection material temperature: nozzle 190℃, second stage 185℃, third stage 180℃, fourth stage 170℃; Mold temperature: 105℃; Injection speed: first stage 40%, second stage 40%; Molding pressure: first stage 80%, second stage 85%; Holding pressure: 60%; Holding time: 1s; Back pressure: 4bar; Cooling time: 10s. After cooling and molding, a blank is obtained.

[0097] S3. Catalytic degreasing: The catalyst is 98% fuming nitric acid, the temperature is 115℃, the acid inlet rate is 5ml / min, and the degreasing time is 300min;

[0098] S4. Sintering Process: The catalytically degreased blank is placed in a graphite vacuum sintering furnace under argon atmosphere (argon flow rate 10 L / min) for sintering. The sintering procedure for the graphite vacuum sintering furnace is as follows:

[0099] ① Heating rate is 5℃ / min, room temperature → 300℃, hold for 30min;

[0100] ② The heating rate is 2℃ / min, from 300℃ to 450℃, and the temperature is maintained for 30 minutes;

[0101] ③ The heating rate is 2℃ / min, from 450℃ to 600℃, and the temperature is maintained for 60 minutes;

[0102] ④ Heating rate is 3℃ / min, 600℃→1050℃, hold for 20min;

[0103] ⑤ The heating rate is 10℃ / min, from 1050℃ to 1250℃, and the temperature is maintained for 120min;

[0104] ⑥ The cooling rate is 7.5℃ / min, from 1250℃ to 800℃;

[0105] ⑦ The cooling rate is 12℃ / min, from 800℃ to 80℃;

[0106] S5. The heat treatment is solution treatment + aging. Solution treatment: Under vacuum conditions, the heating rate is 10℃ / min, the temperature is raised from room temperature to 1080℃, held for 120min, and then naturally cooled to room temperature. The heating rate is 10℃ / min, the temperature is raised from room temperature to 520℃, held for 300min, and then naturally cooled to room temperature to obtain commercial 1750MPa grade martensitic aging steel.

[0107] The difference between Comparative Example 2 and Example 1 is as follows: S6. Air cooling: After 60 minutes, the temperature was reduced from 1360℃ to 900℃. A nitrogen-oxygen mixture was introduced at a flow rate of 15L / min, with an oxygen content of 0.25%v. After continuously introducing the nitrogen-oxygen mixture for 2 hours, the sintered blank was cooled from 900℃ to room temperature. The salt spray protection time of the obtained maraging steel was 2 hours. The surface condition of the maraging steel was: discontinuous film and local pitting corrosion.

[0108] The difference between Comparative Example 3 and Example 1 is as follows: S6. Air cooling: After 60 minutes, the temperature was reduced from 1360℃ to 900℃. A nitrogen-oxygen mixture was introduced at a flow rate of 15L / min, with an oxygen content of 0.35%v. After continuously introducing the nitrogen-oxygen mixture for 2 hours, the sintered blank was cooled from 900℃ to room temperature. The remaining steps were the same. The salt spray protection time of the obtained maraging steel was 2 hours. The surface condition of the maraging steel was: stress spalling and film spalling.

[0109] The difference between Comparative Example 4 and Example 1 is as follows: S7. Aging in heat treatment: Under vacuum conditions, the heating rate is 10℃ / min, the room temperature is raised to 485℃ and held for 13h, then nitrogen gas of 0.2MPa is introduced to cool to room temperature at a cooling rate of 10℃ / min, 485℃→room temperature, and the remaining steps are the same.

[0110] The performance testing method is as follows:

[0111] 1. Mechanical properties were tested in accordance with GB / T 228.1-2010. The testing equipment was the WDW-50 electronic universal testing machine from Jinan Huifa Testing Technology Co., Ltd. The tensile strength, yield strength, maximum force, and elongation of the iron-nickel alloy were measured.

[0112] 2. Corrosion resistance shall be determined according to GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test.

[0113] 3. Density was determined according to GB / T 3850-2015 Density of Dense Sintered Metallic Materials and Hard Alloys.

[0114] Table 1: Performance parameters of martensitic aging steels in Example 1 and Comparative Example 1

[0115]

[0116] In conjunction with Example 1 and Comparative Example 1, and in conjunction with Table 1 and Figures 1-6 , Figures 7-10It can be seen that the high-strength corrosion-resistant martensitic aging steel in this invention has excellent mechanical properties, plasticity and corrosion resistance. It has a tensile strength ≥2000MPa, a yield strength ≥1800MPa, an elongation ≥5.0%, a hardness of 50-52HRC, and a salt spray protection time of 4h. It meets the extreme requirements of high-precision and complex parts in aerospace, medical devices, 3C electronic structural components, marine equipment and other industries for mechanical strength (yield strength ≥1800MPa), plasticity (elongation ≥4%) and salt spray corrosion resistance (≥4h).

[0117] By comparing Example 1 and Comparative Examples 2-3, it can be seen that the high-strength corrosion-resistant maraging steel powder for injection molding in this invention uses 12.8±0.2wt%Cr+0.4±0.02wt%Al+0.06±0.01wt%N as the core film-forming element and forms a dense Cr2O3-CrN-Al2O3 composite passivation film by passing a N2 / O2 (O2 content is 0.3±0.02%v) mixed gas through the sintering cooling section. This effectively improves the corrosion resistance of the maraging steel, with a salt spray protection time of 4 hours and ISO 5 level.

[0118] Table 2: Performance parameters of martensitic aging steels in Example 1 and Comparative Example 4

[0119]

[0120] In conjunction with Example 1 and Comparative Example 4, and in conjunction with Table 2 and Figure 5 , Figure 9 It can be seen that the high-strength, corrosion-resistant martensitic aged steel prepared by the aging process of 440℃×10h+485℃×3h exhibits excellent salt spray protection performance, and its mechanical properties and plasticity are also relatively better. From Figure 5 , Figure 9 It can be seen that the high density of interfacial precipitates and continuous grain boundaries in the martensitic aging steel in Comparative Example 4 will damage the compactness of the passivation film and cause a serious decrease in salt spray protection performance (salt spray protection time 1h); while the martensitic aging steel in Comparative Example 4 has fewer interfacial precipitates and better passivation film compactness, and has good salt spray protection performance (salt spray protection time 4h).

[0121] from Figure 2 and Figure 10 The comparison shows that the high-strength corrosion-resistant martensitic aging steel sintered using the process and formula of this invention has a pore closure rate >99.0% (porosity 0.32%, porosity area = 730.46 μm2), while the martensitic aging steel in Comparative Example 1 has a pore closure rate of 97.07% (porosity 2.93%, porosity area = 6609.24 μm2). Therefore, the high-strength corrosion-resistant martensitic aging steel prepared using the process and formula of this invention has good density, salt spray protection performance and mechanical properties.

[0122] In summary, the high-strength and corrosion-resistant martensitic aging steel powder of this invention is suitable for metal powder injection molding process. The high-strength and corrosion-resistant martensitic aging steel prepared meets the extreme requirements of high-precision and complex parts in aerospace, medical devices, 3C electronic structural components, marine equipment, etc., for strength (yield strength ≥1800MPa), plasticity (elongation 4.0~5.5%), and salt spray corrosion resistance (≥4 hours).

[0123] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-strength corrosion-resistant maraging steel powder for injection molding, characterized in that The mass percentage content of each chemical element of the high-strength corrosion-resistant maraging steel powder for injection molding is as follows: 17-19wt% of Ni, 12-13wt% of Cr, 5.0-5.5wt% of Mo, 1.4-1.6wt% of Ti, 0.3-0.5wt% of Al, 0.05-0.10wt% of N, 0.15-0.30wt% of O, C≤0.02, the balance of Fe, and inevitable impurity elements.

2. The high-strength corrosion-resistant maraging steel powder for injection molding according to claim 1, characterized by The mass percentage content of each chemical element of the high-strength corrosion-resistant maraging steel powder for injection molding is as follows: 17.5-18.5wt% of Ni, 12.6-13.0wt% of Cr, 5.3-5.5wt% of Mo, 1.4-1.5wt% of Ti, 0.38-0.42wt% of Al, 0.05-0.07wt% of N, 0.18-0.24wt% of O, C≤0.02, the balance of Fe, and inevitable impurity elements.

3. A high-strength corrosion-resistant maraging steel powder for injection molding according to claim 1 or 2, characterized in that : said powder for injection moulding of high-strength corrosion-resistant maraging steel is prepared by gas atomization, D 10 from 1 to 2 μm, D 50 from 2 to 10 μm, D 90 from 8 to 15.5 μm, loose density from 3 to 4 g / cm 3 , tapped density from 4.2 to 4.8 g / cm 3 .

4. The high-strength corrosion-resistant maraging steel powder for injection molding according to claim 3, characterized by : said high-strength corrosion-resistant maraging steel powder for injection molding is prepared by a gas atomization method, D 10 is 1.6 ± 0.1 μm, D 50 is 8 ± 0.2 μm, D 90 is 15 ± 0.5 μm, the loose bulk density is 3.2 ± 0.2 g / cm 3 , the tap density is 4.5 ± 0.2 g / cm 3 .

5. A high-strength corrosion-resistant maraging steel prepared using the high-strength corrosion-resistant maraging steel powder for injection molding according to any one of claims 1 to 4, characterized by The high-strength corrosion-resistant maraging steel is made of 90-91wt% of the high-strength corrosion-resistant maraging steel powder for injection molding according to any one of claims 1-4 and 9-10 wt% of a binder through a metal powder injection molding process; The preparation method of the high-strength corrosion-resistant maraging steel is as follows: S1. Preparation of the high-strength corrosion-resistant maraging steel powder for injection molding: S2. Mixing: uniformly mix the high-strength corrosion-resistant maraging steel powder for injection molding in S1 with the binder at a mass ratio of (90-91):(9-10) to obtain a high-strength corrosion-resistant maraging steel feedstock; S3. Injection molding: inject the high-strength corrosion-resistant maraging steel feedstock obtained in S2 into a mold through an injection molding machine, cool and shape to obtain a blank; S4. Catalytic degreasing: the catalyst is 98% fuming nitric acid, the temperature is 110-120℃, the nitric acid feeding amount is 4-6ml / min, and the nitric acid degreasing time is 300±30min; S5. Sintering process: place the blank after catalytic degreasing in a graphite vacuum sintering furnace, under argon gas condition, with an argon gas flow of 5-15L / min, heat to 1350-1400℃ at a rate of 15-20℃ / min, and keep the temperature for 3-5h; S6. Cool to 900℃ at a rate of 6.5-8.4℃ / min, pass in nitrogen-oxygen mixed gas, the flow of the nitrogen-oxygen mixed gas is 10-20L / min, the oxygen content in the nitrogen-oxygen mixed gas is 0.30±0.02%v, and after continuously passing in the nitrogen-oxygen mixed gas for 100-150min, the sintered blank is cooled from 900℃ to room temperature; S7. Heat treatment: ①solid solution repair→②two-stage aging→③nitriding repair, and the high-strength corrosion-resistant maraging steel is obtained; the two-stage aging in S7 is as follows: under vacuum condition, the heating rate is 10±0.5℃ / min, heat from room temperature to 440℃, keep the temperature for 10h; the heating rate is 10±0.5℃ / min, heat from 440℃ to 485℃, keep the temperature for 180min, then pass in nitrogen gas with a pressure of 0.2±0.05MPa to cool to room temperature, and the cooling rate is 10±0.5℃ / min.

6. The high-strength corrosion-resistant maraging steel according to claim 5, characterized in that : The S5. sintering process: the catalytic debinding finished blank is placed in a graphite vacuum sintering furnace, under argon condition, argon flow is 5-15 L / min, temperature is raised to 1360℃ at a rate of 20℃ / min, and the holding time is 3.0h.

7. The high-strength corrosion-resistant maraging steel according to claim 6, characterized in that : The S6. temperature is lowered to 900℃ at a rate of 7.6-7.7℃ / min, nitrogen-oxygen mixed gas is introduced, the flow of the nitrogen-oxygen mixed gas is 15 L / min, the oxygen content in the nitrogen-oxygen mixed gas is 0.30%v, after the nitrogen-oxygen mixed gas is continuously introduced for 120 min, the sintered blank is lowered from 900℃ to room temperature.

8. The high-strength corrosion-resistant maraging steel according to claim 6, characterized in that : The S7. solid solution repair: under vacuum condition, the heating rate is 10±0.5℃ / min, the temperature is raised from room temperature to 1100℃, the holding time is 60 min, then nitrogen gas with a pressure of 0.8±0.05 MPa is introduced to cool to room temperature, and the cooling rate is 20±0.5℃ / min.

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